let name;
{let name='hello';}
console.log(name);
let i;
for(let i=0;i<10;i++);
console.log(i);

// basic data type is invariant
const PI=3.1415926;
// object is variable
const car={type:'BMW',price:500,color:'black'};
console.log(car);
car[price]=200;
car[discount]=true;
console.log(car);
// make object attribute invariant
Object.defineProperty(car,'color',{value:'white',writable:false});
console.log(car);
car.color='black';
console.log(car);
// array is object
const array=[1,2,3];
console.log(array);
array[1]=0;
console.log(array);
